Remember to always duck your head when you dig around in the back of that thing.
You know what? Scratch that... Just wear a helmet for your first month.
Ignore that stupid sliding side door and work out of the back doors instead. Use the floor to set up your next group of stops so you don't have climb up in the back every stop. Also unless you're built like a giraffe your close quarters forward visibility is terrible compared to a package car. Keep in mind you're still a tall vehicle even though it's a pickup truck cab so judging your overhead clearance can be difficult at first. And yeah like @Commercial Inside Release said, watch your head when you're climbing around in the back haha!